Abstract:

The High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite has been providing measurements of the wind field in the stratosphere, mesosphere, and lower thermosphere since November 1991. Mesosphereic temperatures, ozone and O(¹D) densities, and stratospheric aerosol extinctions coefficients, are also retrieved. The instrument characteristics have been carefully monitored by frequent calibrations during the nearly eight years of operation. The instrument sensitivity showed a significant decrease (close to 50% in some caes) during the first seven and a half years of operation which was caused by the piezoelectric-controlled etalons slowly drifting from a parallel slate. A recalibration of the etalons in late 1998 resulted in close to a complete recovery of the instrument sensitivity. The loss of sensitivity was linear with time, with discrete changes occurring at times. Careful modeling of the data permits a determination of the sensitivity as a function of time, allowing the data to be corrected for this systematic effect.